{Modern} Rakdos Aggro

I'd replace Shred-Freak with Ash Zealot who is almost strictly better. I get that your trying to allow for the black mana but I'd run Zealot and take out all your swamps.

Take a look at my Modern Human deck?
http://www.mtgvault.com/lordsunfin/decks/modern-boros-human-2/

Hey im not sure how competetive you aim at being but...

First things first, mono red/wr is probably stronger, but i get set on some colours and lock in too, so i'm gonna take that off the table.

Since you have black you get a few cards, one of which is thoughtseize, as much as thoughseize is loved, inquisition of kozilek is probably better, seeing as you are a burn deck and if you haven't won by turn four you've probably lost, your opponent's 7 drops dont matter xD. Of course in a tron matchup or something you can definitely side in some seizes.

Next up, CUTS. Fanatic of mogis, after seeing a strong run in standard there is some hype about this card, let me tell you in modern, which is even higher on removal than standard and with vexing devil (which they will sacrifice if they cant kill it) your devotion isn't going to get above three (including the one from mogis). A non-hase 4/2 (which will get killed itself) with a lightning bolt attatched is good, but not four mana good. Urborg, you don't want two, you don't consistently need one like a deck running a playset of manlands might and getting a second is killer in a low landcount aggro deck. Terminate and Liliana, these are also iffy, why do you need removal in orded to kill your opponent's face? I am partial to liliana so leave her in, but i would for sure cut the terminates.

To ADD. You need some low curve critters, although red seems best equipped why not give black a go with some Vampire Lacerators or Diregraf Ghouls? Another Blackcleave cliffs, as i said you arent gonna make it to the lategame, and a dual land with no downside that enters untapped turn one is just too great. As stated 4 inquisition of kozilek in the mainboard is good. I like what you have going on with blightning so the only thing left to suggest is more burn, Lava Spikes and are good.

Hey im not sure how competetive you aim at being but...

First things first, mono red/wr is probably stronger, but i get set on some colours and lock in too, so i'm gonna take that off the table.

Since you have black you get a few cards, one of which is thoughtseize, as much as thoughseize is loved, inquisition of kozilek is probably better, seeing as you are a burn deck and if you haven't won by turn four you've probably lost, your opponent's 7 drops dont matter xD. Of course in a tron matchup or something you can definitely side in some seizes.

Next up, CUTS. Fanatic of mogis, after seeing a strong run in standard there is some hype about this card, let me tell you in modern, which is even higher on removal than standard and with vexing devil (which they will sacrifice if they cant kill it) your devotion isn't going to get above three (including the one from mogis). A non-hase 4/2 (which will get killed itself) with a lightning bolt attatched is good, but not four mana good. Urborg, you don't want two, you don't consistently need one like a deck running a playset of manlands might and getting a second is killer in a low landcount aggro deck. Terminate and Liliana, these are also iffy, why do you need removal in orded to kill your opponent's face? I am partial to liliana so leave her in, but i would for sure cut the terminates.

To ADD. You need some low curve critters, although red seems best equipped why not give black a go with some Vampire Lacerators or Diregraf Ghouls? Another Blackcleave cliffs, as i said you arent gonna make it to the lategame, and a dual land with no downside that enters untapped turn one is just too great. As stated 4 inquisition of kozilek in the mainboard is good. I like what you have going on with blightning so the only thing left to suggest is more burn, Lava Spikes and are good.

I like the deck. It is not the typical build you see running around modern, so in that aspect you will not have as many hate cards in peoples sideboards against you. Running some more black card removal in the sideboard would be a great idea, as well as some artifact hate. Affinity is a terrible matchup if your sideboard is not ready for it!
Anyway, +1 from me.
If you have a minute could you check out modern zoo deck? Thanks!

http://www.mtgvault.com/zeppelin/decks/homebrew-zoo/

This mix with black doesnt make any sense. Ash Zealot is useless here. Check this out and comapre:
http://www.mtgvault.com/kefir666/decks/red-fast-burn-pure-evil/

I'd go bust and run dark confidant